/**
 * @file
 *
 * Transmission Control Protocol for IP
 */

/*
 * Copyright (c) 2001-2003 Swedish Institute of Computer Science.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification,
 * are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT
 * SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
 * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
 * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY
 * OF SUCH DAMAGE.
 *
 * This file is part of the lwIP TCP/IP stack.
 *
 * Author: Adam Dunkels <adam@sics.se>
 *
 */


/* tcp.c
 *
 * This file contains common functions for the TCP implementation, such as functinos
 * for manipulating the data structures and the TCP timer functions. TCP functions
 * related to input and output is found in tcp_input.c and tcp_output.c respectively.
 *
 */



#include "lwip/opt.h"
#include "lwip/def.h"
#include "lwip/mem.h"
#include "lwip/memp.h"

#include "lwip/tcp.h"

#include "sysclib.h"

#include "smsutils.h"

#include "thbase.h"

#if LWIP_TCP

/* Incremented every coarse grained timer shot
   (typically every 500 ms, determined by TCP_COARSE_TIMEOUT). */
u32_t tcp_ticks;

const u8_t tcp_backoff[13] =
    {1, 2, 3, 4, 5, 6, 7, 7, 7, 7, 7, 7, 7};

/* The TCP PCB lists. */
struct tcp_pcb_listen *tcp_listen_pcbs; /* List of all TCP PCBs in LISTEN state. */
struct tcp_pcb *tcp_active_pcbs;        /* List of all TCP PCBs that are in a
         state in which they accept or send
         data. */
struct tcp_pcb *tcp_tw_pcbs;            /* List of all TCP PCBs in TIME-WAIT. */

struct tcp_pcb *tcp_tmp_pcb;

static u8_t tcp_timer;

static u16_t tcp_new_port(void);

/*
 * tcp_init():
 *
 * Initializes the TCP layer.
 */

void tcp_init(void)
{
    /* Clear globals. */
    tcp_listen_pcbs = NULL;
    tcp_active_pcbs = NULL;
    tcp_tw_pcbs = NULL;
    tcp_tmp_pcb = NULL;

    /* initialize timer */
    tcp_ticks = 0;
    tcp_timer = 0;
}

/*
 * tcp_tmr():
 *
 * Called periodically to dispatch TCP timers.
 *
 */

void tcp_tmr(void)
{
    /* Call tcp_fasttmr() every 250 ms */
    tcp_fasttmr();

    if (++tcp_timer & 1) {
        /* Call tcp_tmr() every 500 ms, i.e., every other timer
       tcp_tmr() is called. */
        tcp_slowtmr();
    }
}

/*
 * tcp_close():
 *
 * Closes the connection held by the PCB.
 *
 */

err_t tcp_close(struct tcp_pcb *pcb)
{
    err_t err;

#if TCP_DEBUG
    LWIP_DEBUGF(TCP_DEBUG, ("tcp_close: closing in state "));
    tcp_debug_print_state(pcb->state);
    LWIP_DEBUGF(TCP_DEBUG, ("\n"));
#endif /* TCP_DEBUG */
    switch (pcb->state) {
        case LISTEN:
            err = ERR_OK;
            tcp_pcb_remove((struct tcp_pcb **)&tcp_listen_pcbs, pcb);
            memp_free(MEMP_TCP_PCB_LISTEN, pcb);
            pcb = NULL;
            break;
        case SYN_SENT:
            err = ERR_OK;
            tcp_pcb_remove(&tcp_active_pcbs, pcb);
            memp_free(MEMP_TCP_PCB, pcb);
            pcb = NULL;
            break;
        case SYN_RCVD:
        case ESTABLISHED:
            err = tcp_send_ctrl(pcb, TCP_FIN);
            if (err == ERR_OK) {
                pcb->state = FIN_WAIT_1;
            }
            break;
        case CLOSE_WAIT:
            err = tcp_send_ctrl(pcb, TCP_FIN);
            if (err == ERR_OK) {
                pcb->state = LAST_ACK;
            }
            break;
        default:
            /* Has already been closed, do nothing. */
            err = ERR_OK;
            pcb = NULL;
            break;
    }

    if (pcb != NULL && err == ERR_OK) {
        err = tcp_output(pcb);
    }
    return err;
}

/*
 * tcp_abort()
 *
 * Aborts a connection by sending a RST to the remote host and deletes
 * the local protocol control block. This is done when a connection is
 * killed because of shortage of memory.
 *
 */

void tcp_abort(struct tcp_pcb *pcb)
{
    u32_t seqno, ackno;
    u16_t remote_port, local_port;
    struct ip_addr remote_ip, local_ip;
#if LWIP_CALLBACK_API
    void (*errf)(void *arg, err_t err);
#endif /* LWIP_CALLBACK_API */
    void *errf_arg;


    /* Figure out on which TCP PCB list we are, and remove us. If we
     are in an active state, call the receive function associated with
     the PCB with a NULL argument, and send an RST to the remote end. */
    if (pcb->state == TIME_WAIT) {
        tcp_pcb_remove(&tcp_tw_pcbs, pcb);
        memp_free(MEMP_TCP_PCB, pcb);
    } else {
        seqno = pcb->snd_nxt;
        ackno = pcb->rcv_nxt;
        ip_addr_set(&local_ip, &(pcb->local_ip));
        ip_addr_set(&remote_ip, &(pcb->remote_ip));
        local_port = pcb->local_port;
        remote_port = pcb->remote_port;
#if LWIP_CALLBACK_API
        errf = pcb->errf;
#endif /* LWIP_CALLBACK_API */
        errf_arg = pcb->callback_arg;
        tcp_pcb_remove(&tcp_active_pcbs, pcb);
        if (pcb->unacked != NULL) {
            tcp_segs_free(pcb->unacked);
        }
        if (pcb->unsent != NULL) {
            tcp_segs_free(pcb->unsent);
        }
#if TCP_QUEUE_OOSEQ
        if (pcb->ooseq != NULL) {
            tcp_segs_free(pcb->ooseq);
        }
#endif /* TCP_QUEUE_OOSEQ */
        memp_free(MEMP_TCP_PCB, pcb);
        TCP_EVENT_ERR(errf, errf_arg, ERR_ABRT);
        LWIP_DEBUGF(TCP_RST_DEBUG, ("tcp_abort: sending RST\n"));
        tcp_rst(seqno, ackno, &local_ip, &remote_ip, local_port, remote_port);
    }
}

/*
 * tcp_bind():
 *
 * Binds the connection to a local portnumber and IP address. If the
 * IP address is not given (i.e., ipaddr == NULL), the IP address of
 * the outgoing network interface is used instead.
 *
 */

err_t tcp_bind(struct tcp_pcb *pcb, struct ip_addr *ipaddr, u16_t port)
{
    struct tcp_pcb *cpcb;
#ifdef SO_REUSE
    int reuse_port_all_set = 1;
#endif /* SO_REUSE */

    if (port == 0) {
        port = tcp_new_port();
    }
#ifndef SO_REUSE
    /* Check if the address already is in use. */
    for (cpcb = (struct tcp_pcb *)tcp_listen_pcbs;
         cpcb != NULL; cpcb = cpcb->next) {
        if (cpcb->local_port == port) {
            if (ip_addr_isany(&(cpcb->local_ip)) ||
                ip_addr_isany(ipaddr) ||
                ip_addr_cmp(&(cpcb->local_ip), ipaddr)) {
                return ERR_USE;
            }
        }
    }
    for (cpcb = tcp_active_pcbs;
         cpcb != NULL; cpcb = cpcb->next) {
        if (cpcb->local_port == port) {
            if (ip_addr_isany(&(cpcb->local_ip)) ||
                ip_addr_isany(ipaddr) ||
                ip_addr_cmp(&(cpcb->local_ip), ipaddr)) {
                return ERR_USE;
            }
        }
    }
#else  /* SO_REUSE */
    /* Search through list of PCB's in LISTEN state.

  If there is a PCB bound to specified port and IP_ADDR_ANY another PCB can be bound to the interface IP
  or to the loopback address on the same port if SOF_REUSEADDR is set. Any combination of PCB's bound to
  the same local port, but to one address out of {IP_ADDR_ANY, 127.0.0.1, interface IP} at a time is valid.
  But no two PCB's bound to same local port and same local address is valid.

  If SOF_REUSEPORT is set several PCB's can be bound to same local port and same local address also. But then
  all PCB's must have the SOF_REUSEPORT option set.

  When the two options aren't set and specified port is already bound, ERR_USE is returned saying that
  address is already in use. */
    for (cpcb = (struct tcp_pcb *)tcp_listen_pcbs; cpcb != NULL; cpcb = cpcb->next) {
        if (cpcb->local_port == port) {
            if (ip_addr_cmp(&(cpcb->local_ip), ipaddr)) {
                if (pcb->so_options & SOF_REUSEPORT) {
                    LWIP_DEBUGF(TCP_DEBUG, ("tcp_bind: in listening PCB's: SO_REUSEPORT set and same address.\n"));
                    reuse_port_all_set = (reuse_port_all_set && (cpcb->so_options & SOF_REUSEPORT));
                } else {
                    LWIP_DEBUGF(TCP_DEBUG, ("tcp_bind: in listening PCB's: SO_REUSEPORT not set and same address.\n"));
                    return ERR_USE;
                }
            } else if ((ip_addr_isany(ipaddr) && !ip_addr_isany(&(cpcb->local_ip))) ||
                       (!ip_addr_isany(ipaddr) && ip_addr_isany(&(cpcb->local_ip)))) {
                if (!(pcb->so_options & SOF_REUSEADDR) && !(pcb->so_options & SOF_REUSEPORT)) {
                    LWIP_DEBUGF(TCP_DEBUG, ("tcp_bind: in listening PCB's SO_REUSEPORT or SO_REUSEADDR not set and not the same address.\n"));
                    return ERR_USE;
                } else {
                    LWIP_DEBUGF(TCP_DEBUG, ("tcp_bind: in listening PCB's SO_REUSEPORT or SO_REUSEADDR set and not the same address.\n"));
                }
            }
        }
    }

    /* Search through list of PCB's in a state in which they can accept or send data. Same decription as for
     PCB's in state LISTEN applies to this PCB's regarding the options SOF_REUSEADDR and SOF_REUSEPORT. */
    for (cpcb = tcp_active_pcbs; cpcb != NULL; cpcb = cpcb->next) {
        if (cpcb->local_port == port) {
            if (ip_addr_cmp(&(cpcb->local_ip), ipaddr)) {
                if (pcb->so_options & SOF_REUSEPORT) {
                    LWIP_DEBUGF(TCP_DEBUG, ("tcp_bind: in active PCB's SO_REUSEPORT set and same address.\n"));
                    reuse_port_all_set = (reuse_port_all_set && (cpcb->so_options & SOF_REUSEPORT));
                } else {
                    LWIP_DEBUGF(TCP_DEBUG, ("tcp_bind: in active PCB's SO_REUSEPORT not set and same address.\n"));
                    return ERR_USE;
                }
            } else if ((ip_addr_isany(ipaddr) && !ip_addr_isany(&(cpcb->local_ip))) ||
                       (!ip_addr_isany(ipaddr) && ip_addr_isany(&(cpcb->local_ip)))) {
                if (!(pcb->so_options & SOF_REUSEADDR) && !(pcb->so_options & SOF_REUSEPORT)) {
                    LWIP_DEBUGF(TCP_DEBUG, ("tcp_bind: in active PCB's SO_REUSEPORT or SO_REUSEADDR not set and not the same address.\n"));
                    return ERR_USE;
                } else {
                    LWIP_DEBUGF(TCP_DEBUG, ("tcp_bind: in active PCB's SO_REUSEPORT or SO_REUSEADDR set and not the same address.\n"));
                }
            }
        }
    }

    /* Search through list of PCB's in TIME_WAIT state. If SO_REUSEADDR is set a bound combination [IP, port}
     can be rebound. The same applies when SOF_REUSEPORT is set.

     If SOF_REUSEPORT is set several PCB's can be bound to same local port and same local address also. But then
     all PCB's must have the SOF_REUSEPORT option set.

     When the two options aren't set and specified port is already bound, ERR_USE is returned saying that
     address is already in use. */
    for (cpcb = tcp_tw_pcbs; cpcb != NULL; cpcb = cpcb->next) {
        if (cpcb->local_port == port) {
            if (ip_addr_cmp(&(cpcb->local_ip), ipaddr)) {
                if (!(pcb->so_options & SOF_REUSEADDR) && !(pcb->so_options & SOF_REUSEPORT)) {
                    LWIP_DEBUGF(TCP_DEBUG, ("tcp_bind: in TIME_WAIT PCB's SO_REUSEPORT or SO_REUSEADDR not set and same address.\n"));
                    return ERR_USE;
                } else if (pcb->so_options & SOF_REUSEPORT) {
                    LWIP_DEBUGF(TCP_DEBUG, ("tcp_bind: in TIME_WAIT PCB's SO_REUSEPORT set and same address.\n"));
                    reuse_port_all_set = (reuse_port_all_set && (cpcb->so_options & SOF_REUSEPORT));
                }
            }
        }
    }

    /* If SOF_REUSEPORT isn't set in all PCB's bound to specified port and local address specified then
     {IP, port} can't be reused. */
    if (!reuse_port_all_set) {
        LWIP_DEBUGF(TCP_DEBUG, ("tcp_bind: not all sockets have SO_REUSEPORT set.\n"));
        return ERR_USE;
    }
#endif /* SO_REUSE */

    if (!ip_addr_isany(ipaddr)) {
        pcb->local_ip = *ipaddr;
    }
    pcb->local_port = port;
    LWIP_DEBUGF(TCP_DEBUG, ("tcp_bind: bind to port %u\n", port));
    return ERR_OK;
}
#if LWIP_CALLBACK_API
static err_t
tcp_accept_null(void *arg, struct tcp_pcb *pcb, err_t err)
{
    (void)arg;
    (void)pcb;
    (void)err;

    return ERR_ABRT;
}
#endif /* LWIP_CALLBACK_API */

/*
 * tcp_listen():
 *
 * Set the state of the connection to be LISTEN, which means that it
 * is able to accept incoming connections. The protocol control block
 * is reallocated in order to consume less memory. Setting the
 * connection to LISTEN is an irreversible process.
 *
 */

struct tcp_pcb *
tcp_listen(struct tcp_pcb *pcb)
{
    struct tcp_pcb_listen *lpcb;

    /* already listening? */
    if (pcb->state == LISTEN) {
        return pcb;
    }
    lpcb = memp_malloc(MEMP_TCP_PCB_LISTEN);
    if (lpcb == NULL) {
        return NULL;
    }
    lpcb->callback_arg = pcb->callback_arg;
    lpcb->local_port = pcb->local_port;
    lpcb->state = LISTEN;
    lpcb->so_options = pcb->so_options;
    lpcb->so_options |= SOF_ACCEPTCONN;
    lpcb->ttl = pcb->ttl;
    lpcb->tos = pcb->tos;
    ip_addr_set(&lpcb->local_ip, &pcb->local_ip);
    memp_free(MEMP_TCP_PCB, pcb);
#if LWIP_CALLBACK_API
    lpcb->accept = tcp_accept_null;
#endif /* LWIP_CALLBACK_API */
    TCP_REG(&tcp_listen_pcbs, lpcb);
    return (struct tcp_pcb *)lpcb;
}

/*
 * tcp_recved():
 *
 * This function should be called by the application when it has
 * processed the data. The purpose is to advertise a larger window
 * when the data has been processed.
 *
 */

void tcp_recved(struct tcp_pcb *pcb, u16_t len)
{
    if ((u32_t)pcb->rcv_wnd + len > TCP_WND) {
        pcb->rcv_wnd = TCP_WND;
    } else {
        pcb->rcv_wnd += len;
    }
    if (pcb->flags & TF_ACKNODELAY) {
        tcp_ack_now(pcb);
        pcb->flags &= ~(TF_ACK_DELAY | TF_ACK_NOW);
    } else if (!(pcb->flags & TF_ACK_DELAY) &&
               !(pcb->flags & TF_ACK_NOW)) {
        tcp_ack(pcb);
    }

    LWIP_DEBUGF(TCP_DEBUG, ("tcp_recved: recveived %u bytes, wnd %u (%u).\n",
                            len, pcb->rcv_wnd, TCP_WND - pcb->rcv_wnd));
}

/*
 * tcp_new_port():
 *
 * A nastly hack featuring 'goto' statements that allocates a
 * new TCP local port.
 */

static u16_t
tcp_new_port(void)
{
    struct tcp_pcb *pcb;
#ifndef TCP_LOCAL_PORT_RANGE_START
#define TCP_LOCAL_PORT_RANGE_START 4096
#define TCP_LOCAL_PORT_RANGE_END   0x7fff
#endif
    static u16_t port = TCP_LOCAL_PORT_RANGE_START;
    // randomize the port value a bit to avoid TCP conflicts
    // on lost connections
    iop_sys_clock_t tme;
    GetSystemTime(&tme);
    port += (tme.lo) % 8192;

again:
    if (++port > TCP_LOCAL_PORT_RANGE_END) {
        port = TCP_LOCAL_PORT_RANGE_START;
    }

    for (pcb = tcp_active_pcbs; pcb != NULL; pcb = pcb->next) {
        if (pcb->local_port == port) {
            goto again;
        }
    }
    for (pcb = tcp_tw_pcbs; pcb != NULL; pcb = pcb->next) {
        if (pcb->local_port == port) {
            goto again;
        }
    }
    for (pcb = (struct tcp_pcb *)tcp_listen_pcbs; pcb != NULL; pcb = pcb->next) {
        if (pcb->local_port == port) {
            goto again;
        }
    }
    return port;
}

/*
 * tcp_connect():
 *
 * Connects to another host. The function given as the "connected"
 * argument will be called when the connection has been established.
 *
 */

err_t tcp_connect(struct tcp_pcb *pcb, struct ip_addr *ipaddr, u16_t port,
                  err_t (*connected)(void *arg, struct tcp_pcb *tpcb, err_t err))
{
    u32_t optdata;
    err_t ret;
    u32_t iss;

    LWIP_DEBUGF(TCP_DEBUG, ("tcp_connect to port %u\n", port));
    if (ipaddr != NULL) {
        pcb->remote_ip = *ipaddr;
    } else {
        return ERR_VAL;
    }
    pcb->remote_port = port;
    if (pcb->local_port == 0) {
        pcb->local_port = tcp_new_port();
    }
    iss = tcp_next_iss();
    pcb->rcv_nxt = 0;
    pcb->snd_nxt = iss;
    pcb->lastack = iss - 1;
    pcb->snd_lbb = iss - 1;
    pcb->rcv_wnd = TCP_WND;
    pcb->snd_wnd = TCP_WND;
    pcb->mss = TCP_MSS;
    pcb->cwnd = 1;
    pcb->ssthresh = pcb->mss * 10;
    pcb->state = SYN_SENT;
#if LWIP_CALLBACK_API
    pcb->connected = connected;
#endif /* LWIP_CALLBACK_API */
    TCP_REG(&tcp_active_pcbs, pcb);

    /* Build an MSS option */
    optdata = htonl(((u32_t)2 << 24) |
                    ((u32_t)4 << 16) |
                    (((u32_t)pcb->mss / 256) << 8) |
                    (pcb->mss & 255));

    ret = tcp_enqueue(pcb, NULL, 0, TCP_SYN, 0, (u8_t *)&optdata, 4);
    if (ret == ERR_OK) {
        tcp_output(pcb);
    }
    return ret;
}

/*
 * tcp_slowtmr():
 *
 * Called every 500 ms and implements the retransmission timer and the timer that
 * removes PCBs that have been in TIME-WAIT for enough time. It also increments
 * various timers such as the inactivity timer in each PCB.
 */

void tcp_slowtmr(void)
{
    struct tcp_pcb *pcb, *pcb2, *prev;
    u32_t eff_wnd;
    u8_t pcb_remove; /* flag if a PCB should be removed */
    err_t err;

    err = ERR_OK;

    ++tcp_ticks;

    /* Steps through all of the active PCBs. */
    prev = NULL;
    pcb = tcp_active_pcbs;
    if (pcb == NULL)
        LWIP_DEBUGF(TCP_DEBUG, ("tcp_slowtmr: no active pcbs\n"));
    while (pcb != NULL) {
        LWIP_DEBUGF(TCP_DEBUG, ("tcp_slowtmr: processing active pcb\n"));
        LWIP_ASSERT("tcp_slowtmr: active pcb->state != CLOSED\n", pcb->state != CLOSED);
        LWIP_ASSERT("tcp_slowtmr: active pcb->state != LISTEN\n", pcb->state != LISTEN);
        LWIP_ASSERT("tcp_slowtmr: active pcb->state != TIME-WAIT\n", pcb->state != TIME_WAIT);

        pcb_remove = 0;

        if (pcb->state == SYN_SENT && pcb->nrtx == TCP_SYNMAXRTX) {
            ++pcb_remove;
            LWIP_DEBUGF(TCP_DEBUG, ("tcp_slowtmr: max SYN retries reached\n"));
        } else if (pcb->nrtx == TCP_MAXRTX) {
            ++pcb_remove;
            LWIP_DEBUGF(TCP_DEBUG, ("tcp_slowtmr: max DATA retries reached\n"));
        } else {
            ++pcb->rtime;
            if (pcb->unacked != NULL && pcb->rtime >= pcb->rto) {

                /* Time for a retransmission. */
                LWIP_DEBUGF(TCP_RTO_DEBUG, ("tcp_slowtmr: rtime %u pcb->rto %u\n",
                                            pcb->rtime, pcb->rto));

                /* Double retransmission time-out unless we are trying to
                 * connect to somebody (i.e., we are in SYN_SENT). */
                if (pcb->state != SYN_SENT) {
                    pcb->rto = ((pcb->sa >> 3) + pcb->sv) << tcp_backoff[pcb->nrtx];
                }
                tcp_rexmit(pcb);
                /* Reduce congestion window and ssthresh. */
                eff_wnd = LWIP_MIN(pcb->cwnd, pcb->snd_wnd);
                pcb->ssthresh = eff_wnd >> 1;
                if (pcb->ssthresh < pcb->mss) {
                    pcb->ssthresh = pcb->mss * 2;
                }
                pcb->cwnd = pcb->mss;
                LWIP_DEBUGF(TCP_CWND_DEBUG, ("tcp_slowtmr: cwnd %u ssthresh %u\n",
                                             pcb->cwnd, pcb->ssthresh));
            }
        }
        /* Check if this PCB has stayed too long in FIN-WAIT-2 */
        if (pcb->state == FIN_WAIT_2) {
            if ((u32_t)(tcp_ticks - pcb->tmr) >
                TCP_FIN_WAIT_TIMEOUT / TCP_SLOW_INTERVAL) {
                ++pcb_remove;
                LWIP_DEBUGF(TCP_DEBUG, ("tcp_slowtmr: removing pcb stuck in FIN-WAIT-2\n"));
            }
        }

        /* Check if KEEPALIVE should be sent */
        if ((pcb->so_options & SOF_KEEPALIVE) && ((pcb->state == ESTABLISHED) || (pcb->state == CLOSE_WAIT))) {
            if ((u32_t)(tcp_ticks - pcb->tmr) > (pcb->keepalive + TCP_MAXIDLE) / TCP_SLOW_INTERVAL) {
                LWIP_DEBUGF(TCP_DEBUG, ("tcp_slowtmr: KEEPALIVE timeout. Aborting connection to %u.%u.%u.%u.\n",
                                        ip4_addr1(&pcb->remote_ip), ip4_addr2(&pcb->remote_ip),
                                        ip4_addr3(&pcb->remote_ip), ip4_addr4(&pcb->remote_ip)));

                tcp_abort(pcb);
            } else if ((u32_t)(tcp_ticks - pcb->tmr) > (pcb->keepalive + pcb->keep_cnt * TCP_KEEPINTVL) / TCP_SLOW_INTERVAL) {
                tcp_keepalive(pcb);
                pcb->keep_cnt++;
            }
        }

/* If this PCB has queued out of sequence data, but has been
       inactive for too long, will drop the data (it will eventually
       be retransmitted). */
#if TCP_QUEUE_OOSEQ
        if (pcb->ooseq != NULL &&
            (u32_t)tcp_ticks - pcb->tmr >=
                pcb->rto * TCP_OOSEQ_TIMEOUT) {
            tcp_segs_free(pcb->ooseq);
            pcb->ooseq = NULL;
            LWIP_DEBUGF(TCP_CWND_DEBUG, ("tcp_slowtmr: dropping OOSEQ queued data\n"));
        }
#endif /* TCP_QUEUE_OOSEQ */

        /* Check if this PCB has stayed too long in SYN-RCVD */
        if (pcb->state == SYN_RCVD) {
            if ((u32_t)(tcp_ticks - pcb->tmr) >
                TCP_SYN_RCVD_TIMEOUT / TCP_SLOW_INTERVAL) {
                ++pcb_remove;
                LWIP_DEBUGF(TCP_DEBUG, ("tcp_slowtmr: removing pcb stuck in SYN-RCVD\n"));
            }
        }


        /* If the PCB should be removed, do it. */
        if (pcb_remove) {
            tcp_pcb_purge(pcb);
            /* Remove PCB from tcp_active_pcbs list. */
            if (prev != NULL) {
                LWIP_ASSERT("tcp_slowtmr: middle tcp != tcp_active_pcbs", pcb != tcp_active_pcbs);
                prev->next = pcb->next;
            } else {
                /* This PCB was the first. */
                LWIP_ASSERT("tcp_slowtmr: first pcb == tcp_active_pcbs", tcp_active_pcbs == pcb);
                tcp_active_pcbs = pcb->next;
            }

            TCP_EVENT_ERR(pcb->errf, pcb->callback_arg, ERR_ABRT);

            pcb2 = pcb->next;
            memp_free(MEMP_TCP_PCB, pcb);
            pcb = pcb2;
        } else {

            /* We check if we should poll the connection. */
            ++pcb->polltmr;
            if (pcb->polltmr >= pcb->pollinterval) {
                pcb->polltmr = 0;
                LWIP_DEBUGF(TCP_DEBUG, ("tcp_slowtmr: polling application\n"));
                TCP_EVENT_POLL(pcb, err);
                if (err == ERR_OK) {
                    tcp_output(pcb);
                }
            }

            prev = pcb;
            pcb = pcb->next;
        }
    }


    /* Steps through all of the TIME-WAIT PCBs. */
    prev = NULL;
    pcb = tcp_tw_pcbs;
    while (pcb != NULL) {
        LWIP_ASSERT("tcp_slowtmr: TIME-WAIT pcb->state == TIME-WAIT", pcb->state == TIME_WAIT);
        pcb_remove = 0;

        /* Check if this PCB has stayed long enough in TIME-WAIT */
        if ((u32_t)(tcp_ticks - pcb->tmr) > 2 * TCP_MSL / TCP_SLOW_INTERVAL) {
            ++pcb_remove;
        }



        /* If the PCB should be removed, do it. */
        if (pcb_remove) {
            tcp_pcb_purge(pcb);
            /* Remove PCB from tcp_tw_pcbs list. */
            if (prev != NULL) {
                LWIP_ASSERT("tcp_slowtmr: middle tcp != tcp_tw_pcbs", pcb != tcp_tw_pcbs);
                prev->next = pcb->next;
            } else {
                /* This PCB was the first. */
                LWIP_ASSERT("tcp_slowtmr: first pcb == tcp_tw_pcbs", tcp_tw_pcbs == pcb);
                tcp_tw_pcbs = pcb->next;
            }
            pcb2 = pcb->next;
            memp_free(MEMP_TCP_PCB, pcb);
            pcb = pcb2;
        } else {
            prev = pcb;
            pcb = pcb->next;
        }
    }
}

/*
 * tcp_fasttmr():
 *
 * Is called every TCP_FAST_INTERVAL (250 ms) and sends delayed ACKs.
 */

void tcp_fasttmr(void)
{
    struct tcp_pcb *pcb;

    /* send delayed ACKs */
    for (pcb = tcp_active_pcbs; pcb != NULL; pcb = pcb->next) {
        if (pcb->flags & TF_ACK_DELAY) {
            tcp_ack_now(pcb);
            pcb->flags &= ~(TF_ACK_DELAY | TF_ACK_NOW);
        }
    }
}

/*
 * tcp_segs_free():
 *
 * Deallocates a list of TCP segments (tcp_seg structures).
 *
 */

u8_t tcp_segs_free(struct tcp_seg *seg)
{
    u8_t count = 0;
    struct tcp_seg *next;
    while (seg != NULL) {
        next = seg->next;
        count += tcp_seg_free(seg);
        seg = next;
    }
    return count;
}

/*
 * tcp_seg_free():
 *
 * Frees a TCP segment.
 *
 */

u8_t tcp_seg_free(struct tcp_seg *seg)
{
    u8_t count = 0;

    if (seg != NULL) {
        if (seg->p != NULL) {
            count = pbuf_free(seg->p);
#if TCP_DEBUG
            seg->p = NULL;
#endif /* TCP_DEBUG */
        }
        memp_free(MEMP_TCP_SEG, seg);
    }
    return count;
}
#if TCP_QUEUE_OOSEQ

/*
 * tcp_seg_copy():
 *
 * Returns a copy of the given TCP segment.
 *
 */

struct tcp_seg *
tcp_seg_copy(struct tcp_seg *seg)
{
    struct tcp_seg *cseg;

    cseg = memp_malloc(MEMP_TCP_SEG);
    if (cseg == NULL) {
        return NULL;
    }
    mips_memcpy((char *)cseg, (const char *)seg, sizeof(struct tcp_seg));
    pbuf_ref(cseg->p);
    return cseg;
}
#endif

#if LWIP_CALLBACK_API
static err_t
tcp_recv_null(void *arg, struct tcp_pcb *pcb, struct pbuf *p, err_t err)
{
    if (p != NULL) {
        pbuf_free(p);
    } else if (err == ERR_OK) {
        return tcp_close(pcb);
    }
    return ERR_OK;
}
#endif /* LWIP_CALLBACK_API */

static void
tcp_kill_prio(u8_t prio)
{
    struct tcp_pcb *pcb, *inactive;
    u32_t inactivity;
    u8_t mprio;


    mprio = TCP_PRIO_MAX;

    /* We kill the oldest active connection that has lower priority than
     prio. */
    inactivity = 0;
    inactive = NULL;
    for (pcb = tcp_active_pcbs; pcb != NULL; pcb = pcb->next) {
        if (pcb->prio <= prio &&
            pcb->prio <= mprio &&
            (u32_t)(tcp_ticks - pcb->tmr) >= inactivity) {
            inactivity = tcp_ticks - pcb->tmr;
            inactive = pcb;
            mprio = pcb->prio;
        }
    }
    if (inactive != NULL) {
        LWIP_DEBUGF(TCP_DEBUG, ("tcp_kill_prio: killing oldest PCB 0x%p (%ld)\n",
                                (void *)inactive, inactivity));
        tcp_abort(inactive);
    }
}


static void
tcp_kill_timewait(void)
{
    struct tcp_pcb *pcb, *inactive;
    u32_t inactivity;

    inactivity = 0;
    inactive = NULL;
    for (pcb = tcp_tw_pcbs; pcb != NULL; pcb = pcb->next) {
        if ((u32_t)(tcp_ticks - pcb->tmr) >= inactivity) {
            inactivity = tcp_ticks - pcb->tmr;
            inactive = pcb;
        }
    }
    if (inactive != NULL) {
        LWIP_DEBUGF(TCP_DEBUG, ("tcp_kill_timewait: killing oldest TIME-WAIT PCB 0x%p (%ld)\n",
                                (void *)inactive, inactivity));
        tcp_abort(inactive);
    }
}



struct tcp_pcb *
tcp_alloc(u8_t prio)
{
    struct tcp_pcb *pcb;
    u32_t iss;

    pcb = memp_malloc(MEMP_TCP_PCB);
    if (pcb == NULL) {
        /* Try killing oldest connection in TIME-WAIT. */
        LWIP_DEBUGF(TCP_DEBUG, ("tcp_alloc: killing off oldest TIME-WAIT connection\n"));
        tcp_kill_timewait();
        pcb = memp_malloc(MEMP_TCP_PCB);
        if (pcb == NULL) {
            tcp_kill_prio(prio);
            pcb = memp_malloc(MEMP_TCP_PCB);
        }
    }
    if (pcb != NULL) {
        mips_memset(pcb, 0, sizeof(struct tcp_pcb));
        pcb->prio = TCP_PRIO_NORMAL;
        pcb->snd_buf = TCP_SND_BUF;
        pcb->snd_queuelen = 0;
        pcb->rcv_wnd = TCP_WND;
        pcb->tos = 0;
        pcb->ttl = TCP_TTL;
        pcb->mss = TCP_MSS;
        pcb->rto = 3000 / TCP_SLOW_INTERVAL;
        pcb->sa = 0;
        pcb->sv = 3000 / TCP_SLOW_INTERVAL;
        pcb->rtime = 0;
        pcb->cwnd = 1;
        iss = tcp_next_iss();
        pcb->snd_wl2 = iss;
        pcb->snd_nxt = iss;
        pcb->snd_max = iss;
        pcb->lastack = iss;
        pcb->snd_lbb = iss;
        pcb->tmr = tcp_ticks;

        pcb->polltmr = 0;

#if LWIP_CALLBACK_API
        pcb->recv = tcp_recv_null;
#endif /* LWIP_CALLBACK_API */

        /* Init KEEPALIVE timer */
        pcb->keepalive = TCP_KEEPDEFAULT;
        pcb->keep_cnt = 0;
    }
    return pcb;
}
#if LWIP_CALLBACK_API

/*
 * tcp_recv():
 *
 * Used to specify the function that should be called when a TCP
 * connection receives data.
 *
 */

void tcp_recv(struct tcp_pcb *pcb,
              err_t (*recv)(void *arg, struct tcp_pcb *tpcb, struct pbuf *p, err_t err))
{
    pcb->recv = recv;
}

/*
 * tcp_sent():
 *
 * Used to specify the function that should be called when TCP data
 * has been successfully delivered to the remote host.
 *
 */

void tcp_sent(struct tcp_pcb *pcb,
              err_t (*sent)(void *arg, struct tcp_pcb *tpcb, u16_t len))
{
    pcb->sent = sent;
}

/*
 * tcp_err():
 *
 * Used to specify the function that should be called when a fatal error
 * has occured on the connection.
 *
 */

void tcp_err(struct tcp_pcb *pcb,
             void (*errf)(void *arg, err_t err))
{
    pcb->errf = errf;
}
void tcp_accept(struct tcp_pcb *pcb,
                err_t (*accept)(void *arg, struct tcp_pcb *newpcb, err_t err))
{
    ((struct tcp_pcb_listen *)pcb)->accept = accept;
}
#endif /* LWIP_CALLBACK_API */


/*
 * tcp_poll():
 *
 * Used to specify the function that should be called periodically
 * from TCP. The interval is specified in terms of the TCP coarse
 * timer interval, which is called twice a second.
 *
 */

void tcp_poll(struct tcp_pcb *pcb,
              err_t (*poll)(void *arg, struct tcp_pcb *tpcb), u8_t interval)
{
#if LWIP_CALLBACK_API
    pcb->poll = poll;
#endif /* LWIP_CALLBACK_API */
    pcb->pollinterval = interval;
}

/*
 * tcp_pcb_purge():
 *
 * Purges a TCP PCB. Removes any buffered data and frees the buffer memory.
 *
 */

void tcp_pcb_purge(struct tcp_pcb *pcb)
{
    if (pcb->state != CLOSED &&
        pcb->state != TIME_WAIT &&
        pcb->state != LISTEN) {

        LWIP_DEBUGF(TCP_DEBUG, ("tcp_pcb_purge\n"));

        if (pcb->unsent != NULL) {
            LWIP_DEBUGF(TCP_DEBUG, ("tcp_pcb_purge: not all data sent\n"));
        }
        if (pcb->unacked != NULL) {
            LWIP_DEBUGF(TCP_DEBUG, ("tcp_pcb_purge: data left on ->unacked\n"));
        }
#if TCP_QUEUE_OOSEQ /* LW */
        if (pcb->ooseq != NULL) {
            LWIP_DEBUGF(TCP_DEBUG, ("tcp_pcb_purge: data left on ->ooseq\n"));
        }

        tcp_segs_free(pcb->ooseq);
        pcb->ooseq = NULL;
#endif /* TCP_QUEUE_OOSEQ */
        tcp_segs_free(pcb->unsent);
        tcp_segs_free(pcb->unacked);
        pcb->unacked = pcb->unsent = NULL;
    }
}

/*
 * tcp_pcb_remove():
 *
 * Purges the PCB and removes it from a PCB list. Any delayed ACKs are sent first.
 *
 */

void tcp_pcb_remove(struct tcp_pcb **pcblist, struct tcp_pcb *pcb)
{
    TCP_RMV(pcblist, pcb);

    tcp_pcb_purge(pcb);

    /* if there is an outstanding delayed ACKs, send it */
    if (pcb->state != TIME_WAIT &&
        pcb->state != LISTEN &&
        pcb->flags & TF_ACK_DELAY) {
        pcb->flags |= TF_ACK_NOW;
        tcp_output(pcb);
    }
    pcb->state = CLOSED;

    LWIP_ASSERT("tcp_pcb_remove: tcp_pcbs_sane()", tcp_pcbs_sane());
}

/*
 * tcp_next_iss():
 *
 * Calculates a new initial sequence number for new connections.
 *
 */

u32_t tcp_next_iss(void)
{
    static u32_t iss = 6510;

    iss += tcp_ticks; /* XXX */
    return iss;
}

#endif /* LWIP_TCP */
